1. Field of the Invention
The present invention relates to a flap hinge mechanism for attaching a flap to a helicopter rotor blade, as well as a method for manufacturing the same, and relates to a flap hinge apparatus.
2. Description of the Related Art
Rotation of a helicopter rotor blade causes a centrifugal force action proportional to the distance from the rotor center and to the square of the rotational velocity of the rotor, and the centrifugal force can reach approximately 800 G at the tip of the blade. When the rotor blade is provided with a flap, a centrifugal force dependent on the mass thereof will act on the center of mass of the flap. In the flap hinge mechanism, angular displacement motion of the flap should be ensured despite the large centrifugal force and the centrifugal moment corresponding to the distance from the hinge axis to the center of mass of the flap.
When the flap hinge mechanism is configured from a bearing or other such mechanical shaft support, the size and weight of the shaft support increases due to the large thrust load created by the centrifugal force. Because the flap is typically mounted at the trailing edge of the blade, the space available for!mounting of the hinge mechanism will naturally be limited. In particular, because the hinge mechanism cannot be allowed to protrude excessively from the blade surface due to aerodynamic concerns, a thin hinge mechanism will be required. Decreased hinge performance resulting from designs emphasizing thinness of the hinge can then lead to increased size and weight of the actuator for driving the flap. There is thus the problem of the difficulty in achieving both mechanism thinness and support of the centrifugal force.
One possible approach, instead of such mechanical shaft support, would be to adopt a hinge mechanism in the form of a metal plate spring which makes use of elastic deformation. For the fatigue strength to withstand cyclical angular displacement vibration of the flap and in order to prevent actuator drive force losses, however, it would be necessary to form a portion of low stiffness having a certain spring length or more, but doing so would create a tendency toward flexural deformation in the out of plane direction of the plate spring, and shifting of the axis of angular displacement would make precise control of the flap difficult.
The object of the invention is to provide a flap hinge mechanism that can be made thin and light and yet allow achievement of smooth flap motion in spite of large centrifugal forces and a method for manufacturing the same as well as a flap hinge apparatus.
The invention provides a flap hinge mechanism for attaching a flap to a helicopter rotor blade, comprising:
a blade-secured portion secured to the blade,
a flap-secured portion secured to the flap, and
a coupling portion for coupling the blade-secured portion and the flap-secured portion so as to permit angular displacement,
wherein the mechanism is constructed of a composite material in which fibers of the blade-secured portion and flap-secured portion are impregnated with a matrix, and fibers of the coupling portion are not impregnated with a matrix.
In accordance with the invention, by constructing the flap hinge mechanism of a composite material wherein fibers of the blade-secured portion and flap-secured portion are impregnated with a matrix, a member which is light but has high strength can be obtained. Furthermore, as a result of the fact that the fibers of the coupling portion are not impregnated with a matrix, it is possible to impart the flap hinge mechanism with hinge properties of high strength and flexibility.
Furthermore, when the rotor blade rotates and centrifugal forces act on the flap, large centrifugal forces can be supported due to the tensile strength of the fibers of the coupling portion.
Furthermore, the invention provides a flap hinge mechanism for attaching a flap to a helicopter rotor blade, comprising:
a blade-secured portion secured to the blade,
a flap-secured portion secured to the flap, and
a coupling portion for coupling the blade-secured portion and the flap-secured portion so as to permit angular displacement,
wherein the mechanism is constructed of a composite material in which fibers of the blade-secured portion and flap-secured portion are impregnated with a first matrix, and fibers of the coupling portion are impregnated with a second matrix lower in stiffness than the first matrix.
In accordance with the invention, by constructing the flap hinge mechanism of a composite material such that the fibers of the blade-secured portion and flap-secured portion are impregnated with the first matrix, a member which is light but has high strength can be obtained. Furthermore, as a result of the fact that the fibers of the coupling portion are impregnated with the second matrix lower in stiffness than the first matrix, it is possible to impart the flap hinge mechanism with hinge properties of high strength and flexibility.
Furthermore, when the rotor blade rotates and centrifugal forces act on the flap, large centrifugal forces can be supported as a result of the tensile strength of the fibers of the coupling portion.
Furthermore, in the invention it is preferable that the coupling portion includes fibers for which an angle of intersection a between a direction of the fibers and a blade span direction is 10xc2x0 to 45xc2x0.
In accordance with the invention, causing the angle of intersection a between the direction of fibers of the coupling portion and the blade span direction to be 10xc2x0 to 45xc2x0 makes it possible for 98% (=cos 10xc2x0) to 70% (=cos 45xc2x0) of the forces acting to the fibers of the coupling portion to support the centrifugal force while maintaining the softness of the hinge.
Furthermore, the coupling portion may be constructed of unidirectional fibrous sheeting, two-dimensional woven material, or three-dimensional woven material, in monolayer form or as a laminated combination thereof In the case where a plurality of fiber directions are present, the tensile load component acting to support the centrifugal force will be greater for fibers having smaller angles of intersection xcex1.
Furthermore, in the invention it is preferable that the coupling portion is formed of woven fabric. In accordance with the invention, by forming the coupling portion of woven fabric wherein warp and weft are woven together, it is possible to ensure softness of the hinge while increasing strength with respect to loads acting within the plane of the woven fabric.
Furthermore, in the invention it is preferable that a relationship represented by the following expression is satisfied:
0 less than d xcex94xcex8xc2x7xcex1
wherein d is a length of the coupling portion, xcex94xcex8 is an error in a set flap angle, and a is a length of a flap horn arm. In accordance with the invention, because, if the length d of the coupling portion becomes too large, hinge softness will increase and there is a tendency for flexural deformation in the out of plane direction to occur, as a strategy to prevent this, the length d of the coupling portion is set so as to be not more than the product of the flap angle setting error xcex94xcex8 and the flap horn arm length a, permitting prevention of out of plane flexural deformation.
Furthermore, the invention provides a method for manufacturing a flap hinge mechanism for attaching a flap to a helicopter rotor blade comprising a blade-secured portion secured to the blade, a flap-secured portion secured to the flap, and a coupling portion coupling the blade-secured portion and the flap-secured portion so as to permit angular displacement. The method comprises the steps of:
impregnating an area of a woven fabric to be the coupling portion with a soft resin;
impregnating areas of a woven fabric to be the blade-secured portion and the flap-secured portion with an adhesive; and
placing a distance adjustment jig between the blade and the flap and adhesively securing the blade-secured portion and the blade to adhesively secure the flap-secured portion and the flap together.
In accordance with the invention, as a result of previously impregnating with a soft resin the area to be the coupling portion, in coupling the woven fabric of the blade and the woven fabric of the flap, it is possible to ensure the softness of the hinge mechanism since prevention of permeation of adhesive into the coupling portion is permitted. Furthermore, as a result of placement of the distance adjustment jig between the blade and the flap, arbitrary adjustment of the gap between the blade and the flap is permitted, and improvement in the precision of the positioning of the blade and the flap, e.g., parallelism or the like, is permitted.
The adhesive functions as the first matrix for the blade-secured portion and the flap-secured portion, and the soft resin functions as the second matrix for the coupling portion, the overall hinge mechanism consequently being constructed of a composite material.
Furthermore, the invention provides a flap hinge apparatus for attaching a flap to a helicopter rotor blade, comprising:
a composite-material hinge portion constructed of a composite material, for coupling the blade and the flap so as to permit angular displacement; and
a mechanical hinge portion for coupling the blade and the flap so as to permit angular displacement about the same hinge axis as that of the composite-material hinge portion.
In accordance with the invention, the composite-material hinge portion supports the bulk of the centrifugal force, and the mechanical hinge portion prevents out of plane flexural deformation of the composite-material hinge portion. Whereas the composite-material hinge portion permits imparting of hinge properties of high strength and flexibility but is susceptible to radial deviation of axis due to out of plane flexural deformation, the mechanical hinge portion is free from concern with respect to radial deviation of axis but increases in size and weight would be unavoidable if increased strength were to be attempted with the mechanical hinge portion alone. Accordingly, combined use of both so that the mutual strengths and weaknesses compensate for each other permits attainment of a hinge mechanism that is high in strength and yet thin and light, and permits attainment of smooth flap motion despite the presence of centrifugal forces.
Furthermore, in the invention it is preferable that the mechanical hinge portion is composed of a bearing. In accordance with the invention, composing the mechanical hinge portion of a bearing permits a small and light yet stable hinge axis to be obtained but also permits definitive prevention of out of plane flexural deformation at the composite-material hinge portion.
Furthermore, in the invention it is preferable that the mechanical hinge portion is composed of a first elastic member for coupling a top surface of the blade and a bottom surface of the flap, and a second elastic member for coupling a bottom surface of the blade and a top surface of the flap. In accordance with the invention, use of a plurality of elastic members so as to couple the top surface of the blade and the bottom surface of the flap, and the bottom surface of the blade and the top surface of the flap, so as to form an intersection in an x-shaped fashion, makes it possible to obtain a hinge mechanism wherein an intersection portion of the elastic members serves as hinge axis. Because there is no sliding component in such a hinge mechanism, it excels in endurance and in its capacity for reductions in size and weight, while also permitting definitive prevention of out of plane flexural deformation of the composite-material hinge portion due to the restoring force of the elastic member.